Power Considerations

Step 10: Determine ECL Static Power PEO

The equation used by the AMCC MacroMatrix ERC software to compute ECL
static power dissipation for ECL outputs is:

PEO = XXmA * 1.3V * NUMBER_OF_ECL_OUTPUTS

where XX is the current based on the termination

The 1.3V term represents the average between VOH and VOL. This is considered
to be the statistical worst-case for this function

If there is more than one termination, the power for each type of termination
is computed and summed to find the total PECL outputs

ECL Output Termination Current

Table 7-15 provides the ECL output termination currents used by the AMCC
MacroMatrix ERC software. The currents shown are the average current (average
of IOH and IOL)

AMCC automated ECL static power is computed with the 50 or 25 ohm termination
under the assumption of 50% terminations active. This is because AMCC
provides macros that drive 50 ohm loads and macros that drive 25 ohm loads.
These assumptions may vary with the vendor.

Table 7-15 ECL Termination Current

ohm

mA

25

28.0

50

14.0

100

7.0

200

3.5

* the average current (average of IOH and IOL) for termination to -2V

* When 50 ohm or 25 ohm Terminations are Not Used

Resistive loads that differ from that used by automation software will
require manual computation. These loads should be identified when performing
design submission to any vendor.

If other ECL output load resistances are used, the actual current value
must be computed for use in the ECL static power equation. For a -2V termination,
to find the average current in mA, use the following equation.

I in mA = 0.7/( R * (10-3)) for any R

* When VT Ê -2V

For other termination voltages, an adjustment to the power dissipation
computation must be made by the designer. For a termination voltage VT,
to find the average current in mA, use the following equation.

I in mA = (-1.3V - VT)/( R * (10-3)) for any R

* Darlington ECL Outputs

Darlington ECL outputs are treated as a standard ECL outputs for static
power computations.

* On-Chip Series Termination

There is no IOEF output current for on-chip series termination ECL output
macros. All current (power) dissipated is specified in the macro docu-mentation.

Step 11: Sum the Result - Total DC power

Sum the results of the macro and overhead current power computations
with any ECL output macro static power dissipation to obtain the total
worst-case DC power dissipation for the circuit:

PdDC = PCCDC + PEEDC + PEO

The result is the total worst-case DC power dissipated by the circuit
on the target array.

Exercises

Determine how current or power is specified for an array series of
interest. Is it worst-case? If not, find out how the data is converted
to worst-case for Commercial and for Military operating conditions.

Determine how overhead current is accounted for by this array series.
Is it variable? If so, determine what affects it, e.g., number of I/O
by type or their placement.

What other adjustments are required before a final DC power value
can be obtained? If the manual is not specific, consult the vendor.

AMCC Q20000 Exercise. A 100% ECL circuit has been designed using
the Q20080 (8K) array. It uses the following example values:

Macro Name:

Number Used:

Current: IEE mA

FF10S

32

0.98

FF46S

32

0.93

GT09S

0

0.39

GT55D

4

0.91

GT60L

6

0.64

GT60S

6

0.78

GT87D

2

0.49

IE31H

1

2.20

IE93S

82

1.03

IEVCC

9

0.00

MX21S

20

0.66

OE42S

69

8.72

Typical current is specified for one occurrence of each macro. The
power supply is nominal -5.2V. The circuit is military. Compute its
DC power dissipation given the above portion of the macro occurrence
table and the other tables provided in the text. [Ans.: 8.32 Watts
(1994 data)]

Substitute 32 OE14S macros that use 6.69 mA each for 64 of the OE42S
macros and delete one of the GT87D macros. Now how much power is dissipated?